A theory of gelation in finite systems is being developed in order to circumvent the difficulties that have beset the application of Flory-Stockmayer theory to the gel phase. Such "gelling" processes as the condensation of water vapor, the clotting of blood and the formation of antigen-antibody complexes are under consideration. The model for liquid water derived from consideration of both vapor condensation and crystal melting is being applied to the problem of the nature of the "hydrophobic bond" stabilizing the structures of proteins, nucleic acids and membranes. The remarkable dielectric properties of DNA solutions are being studied over a wide range of frequencies, molecular weights, and ionic strengths. A thermodynamic theory for systems containing interfaces and/or field-induced density gradients is being developed. Its application to such problems as the structure and stability of membranes and the profile of density gradient centrifugation may be considered.